UNIVERSITY OF CALIFORNIA
COLLEGE OF AGRICULTURE
AGRICULTURAL EXPERIMENT STATION
BERKELEY, CALIFORNIA
CIRCULAR 347
DECEMBER, 1938
THE WATER-CULTURE METHOD FOR GROWING
PLANTS WITHOUT SOIL
D. R. HOAGLAND1 and D. I. ARNON2
FOREWORD
For approximately a quarter of a century, the California Agricultural
Experiment Station has conducted investigations of problems of plant
nutrition with the use of water-culture technique for growing plants,
as one important method of experimentation. The objective has been to
gain a better understanding of fundamental factors which govern plant
growth, in order to deal more effectively with the many complex ques-
tions of soil and plant interrelations arising in the field. Many workers
have participated in these investigations. One of them, Dr. W. F. Gericke,
conceived the idea some time ago that the water-culture method, hitherto
employed only for scientific studies, might be adapted to commercial use,
and proceeded to devise special technique for this purpose.
This development was soon given widespread publicity in newspapers,
Sunday supplements, and popular journals. The possibility of growing
plants in a medium other than soil intrigued many persons, and soon
extravagant claims were being made by many of the most ardent pro-
ponents of the commercial use of the water-culture method. Further-
more, amateur gardeners sought to make this method a new hobby.
Thousands of inquiries came to the University of California for detailed
information for general application of the water-culture method to com-
mercial as well as to amateur gardening.
Because of doubts expressed concerning many claims made for the use
of the water-culture method as a means of crop production, it became
evident that an independent appraisal of this method of growing crops
was highly desirable. I therefore requested Professor D. R. Hoagland
1 Professor of Plant Nutrition and Chemist in the Experiment Station.
2 Instructor in Truck Crops and Junior Plant Physiologist in the Experiment
Station.
[1]
2 University of California — Experiment Station
and Dr. D. I. Anion to conduct certain additional investigations and to
prepare a manuscript for a popular circular on the general subject of
the growth of plants in water culture.
In view of the complexity of the whole problem of the use of the water-
culture method commercially or by amateurs, the Station can make no
general recommendations at the present time. Those who wish to experi-
ment with the water-culture method on their own responsibility, how-
ever, are entitled to the benefit of such information as is now available
from the researches of the Station.
The purpose of this circular is to present that information.
C. B. Hutchison, Director
Agricultural Experiment Station
CONTENTS page
Foreword 1
Introduction 3
Historical sketch of the development of the water-culture method 4
Principles and application of the water-culture method 10
Importance of climatic requirements 10
Temperature relations 11
Comparison of yields by soil and water culture 11
Nutritional quality of plant product 15
Present status of the commercial water-culture method 16
Growing of plants in water culture by amateurs 18
Use of prepared salt mixtures 18
Composition of nutrient solutions 23
Nutrient requirements of different kinds of plants 24
Nutrient deficiencies, insect attacks, and diseases 26
Water requirements of plants grown by the water-culture method 26
Resume1 of the water-culture technique 26
Directions for growing plants by the water-culture method 29
Tanks and other containers for nutrient solutions 29
Nature of bed 31
Planting procedures 31
Spacing of plants 32
Addition of water to tanks 32
Changes of nutrient solution 33
Testing and adjusting the acidity of water and nutrient solution 33
Modification of nutrient solution based on analysis of water 34
Selection of a nutrient solution 34
Preparation of nutrient solutions: method A, for amateurs 35
Preparation of nutrient solutions: method B, for schools or technical
laboratories 36
Nutrient solutions for use in demonstrating mineral deficiencies in plants .... 38
Cm. 347] Water- Culture Method 3
INTRODUCTION
During the past few years, the popular press has given an immense
amount of publicity to the subject of commercial or amateur growing
of crops in "water culture", that is, growing plants with their roots in
a solution containing the mineral nutrients essential for plant growth.
The solution takes the place of soil in supplying water and mineral nu-
trients to the plant. This method of growing plants is also described
under such names as "tray agriculture," "tank farming," and the re-
cently coined term, "hydroponics." Frequently, popular accounts of
recent experiments on growing plants by the water-culture method leave
the reader with the impression that a new discovery has been made which
bids fair to revolutionize present methods of crop production, and indeed
promises to produce in the future far-reaching social dislocations by dis-
pensing with the soil as a medium for growing many crops.
Wholly unfounded claims have been made by promoters that a new
"profession of soilless farming" has been developed, which affords ex-
traordinary opportunities for investment of time and funds. Attempts
have been made to convince the public that a short course of training will
give preparation for entering this new "profession." The impression has
been given also that the water-culture method offers an easy means of
raising food for household use.
Some of the popular articles on the water-culture method of crop pro-
duction are grossly inaccurate in fact and misleading in implication.
Widely circulated rumors, claims, and predictions about the water-
culture production of crops often have little more to commend them than
the author's unrestrained imagination. Erroneous and even fantastic
ideas have been conceived that betray a lack of knowledge of elementary
principles of plant physiology. For example, there have been statements
that in the future most of the food needed by the occupants of a great
apartment building may be grown on the roof, and that in large cities
"skyscraper" farms may supply huge quantities of fresh fruit and vege-
tables. One Sunday-supplement article contained an illustration show-
ing a housewife opening a small closet off the kitchen and picking
tomatoes from vines growing in water culture with the aid of electric
lights. There has even arisen a rumor that the restaurants of a large
chain in New York City are growing their vegetables in basements.
Stories of this kind have gained wide currency and have captured the
imagination of many persons. Many factors have doubtless contributed
to arousing the surprisingly wide interest in the water-culture method of
crop production. The psychological effect of current discussion of the
4 University of California — Experiment Station
wastage of soil resources through soil erosion and depletion has made
the public especially receptive to new ideas relating to crop production.
Some people have been impressed by the assumed social and economic
significance of the water-culture method. Others, moved by the common
delight of mankind in growing plants, even though the garden space is
reduced to a window sill, have sought directions to enable them to try a
novel technique of plant culture. The consequence of the discussion of
this method has been the creation of a great public demand for more
specific information. Should this newly aroused interest in plant growth
lead to a greater diffusion of knowledge of certain general principles of
plant physiology, the publicity regarding the water-culture method of
crop production might in the long run have a beneficial effect. Growing
plants in water culture has been considered by some popular writers as
a "marvel of science." The growth of plants is indeed marvelous, but not
more so when plants are grown in water culture than when they are
grown in soil.
Sometimes two entirely distinct lines of investigation at the California
Agricultural Experiment Station, in which the water-culture technique
is used, have been confused in popular discussions. One of these concerns
methods of growing plants in water culture under natural light, the other
the study of special scientific problems of plant growth in controlled
chambers artificially illuminated. It is economically impossible at the
present time to grow crops commercially solely under artificial illumina-
tion, even if there were any reason for doing so. At several other institu-
tions, considerable attention has been devoted to study of the effect of
supplementing daylight with artificial light during some seasons of the
year, to control the flowering period or to accelerate growth of certain
kinds of plants (particularly floral plants) in greenhouses, but this prac-
tice has mainly been applied so far to plants developed in soil and has no
essential relation to the water-culture method of growing plants.
HISTORICAL SKETCH OF THE DEVELOPMENT OF THE
WATER-CULTURE METHOD
Curiously enough, the earliest recorded experiment with water cultures
was carried out in search of a so-called "principle of vegetation" in a day
when so little was known about the principles of plant nutrition that
there was little chance of profitable results from such an experiment.
Woodward in 1699 grew spearmint in several kinds of water : rain, river,
and conduit water to which he in one case added garden mold. He found
that the greatest increase in the weight of the plant took place in the
water containing the greatest admixture of soil. His conclusion was
Cib. 347] Water- Culture Method 5
"That earth, and not water, is the matter that constitutes vegetables."
The real development of the technique of water culture took place
about three-quarters of a century ago. It came as a logical result of the
modern concepts of plant nutrition. By the middle of the nineteenth cen-
tury, enough of the fundamental facts of plant physiology had been ac-
cumulated and properly evaluated to enable the botanists and chemists
of that period to correctly assign to the soil the part which it plays in the
nutrition of plants. They realized that plants are made of chemical ele-
ments obtained from three sources : air, water, and soil ; and that the
plants grow and increase in size and weight by combining these elements
into various plant substances.
Water is, of course, always the main component of growing plants.
But the major portion, usually about 90 per cent, of the dry matter of
most plants is made up of three chemical elements : carbon, oxygen, and
hydrogen. Carbon comes from the air, oxygen from the air and from
water, and hydrogen from water. In addition to the three elements
named above, plants contain other elements, such as nitrogen, phosphor-
ous, potassium, and calcium, which they obtain from the soil. The soil,
then, supplies to the plant a large number of chemical elements, but they
constitute only a very small portion of the plant. Yet various elements
which occur in plants in comparatively small amounts are just as essen-
tial to growth as those which compose the bulk of plant tissues.
The publication, in 1840, of Liebig's book on the application of organic
chemistry to agriculture and physiology,3 in which the above views were
ably and effectively brought to the attention of plant physiologists and
chemists of that period, served as a great stimulus for the undertaking of
experimental work in plant nutrition. (Liebig, however, failed to under-
stand the role of soil as a source of nitrogen for plants, and the fixation
of atmospheric nitrogen by nodule organisms was not then known.)
Once it was recognized that the function of the soil in the economy of
the plant is to furnish certain chemical elements, as well as water, it was
but natural to attempt to supply these elements and water independently
of soil. The credit for initiating exact experimentation in this field be-
longs to the French chemist, Jean Boussignault, who is regarded as the
founder of modern methods of conducting experiments in vegetation.
Boussignault, who had begun his experiments on plants even before
1840, grew them in insoluble artificial soils: sand, quartz, and sugar
charcoal, which he watered with solutions of known composition. His
results provided experimental verification for the mineral theory of
8 Liebig, Justus von. Chemistry in its applications to agriculture and physiology.
[English translation.] 401 p. John Wiley and Sons, New York, N. Y. 1861.
University of California — Experiment Station
plant nutrition as put forward by Liebig, and were at once a demonstra-
tion of the feasibility of growing plants in a medium other than a "nat-
ural soil." This method of growing plants in artificial insoluble soils was
later improved by Salm-Horstmar (1856-1860) and has been used
since, with various technical improvements, by nu-
merous investigators throughout the world. In recent
years, large-scale techniques have been devised for
growing plants for experimental or commercial pur-
poses in beds of sand or other inert solid material.
After plants were successfully grown in artificial
culture media, it was but one more step to dispense
with any solid medium and attempt to grow plants in
water to which the chemical elements required by
plants were added. This was successfully accom-
plished in 1860 by Sachs and about the same time by
Knop. To quote Sachs directly :
In the year 1860, I published the results of experiments
which demonstrated that land plants are capable of absorbing
their nutritive matters out of watery solutions, without the aid
of soil, and that it is possible in this way not only to maintain
plants alive and growing for a long time, as had long been
known, but also to bring about a vigorous increase of their
organic substance, and even the production of seed capable of
germination.4
The original technique developed by Sachs for
growing plants in nutrient solutions is still widely
used, essentially unaltered. He germinated the seed
in well-washed sawdust, until the plants reached a
size convenient for transplanting. After carefully re-
moving and washing the seedling, he fastened it into
a perforated cork, with the roots dipping into the
solution. The complete assembly is shown in figure 1,
which is a reproduction of Sachs's illustration.
Since the publication of Sachs's standard solution
formula (table 1) for growing plants in water cul-
ture, many other formulas have been suggested and widely used with
success by many investigators in different countries. Knop, who under-
took water-culture experiments at the same time as Sachs, proposed in
1865 a nutrient solution, which became one of the most widely employed
in studies of plant nutrition. Other formulas for nutrient solutions have
1 Sachs, Julius von. Lectures on the physiology of plants. 836 p. Clarendon Press,
Oxford. 1887.
Fig. 1. — Water-
culture installation
employed by the
plant physiologist
Sachs in the middle
of the last century.
(Reproduced from
Sachs, Lectures on
the Physiology of
Plants, Clarendon
Press, 1887.)
Cir. 347 J
Water- Culture Method
been proposed by Tollens in 1882, by Schimper in 1890, by Pfeffer in
1900, by Crone in 1902, by Tottingham in 1914, by Shive in 1915, by
Hoagland in 1920, and many others.
At the very inception of the water-culture work, investigators clearly
recognized that there can be no one composition of a nutrient solution
which is always superior to every other composition, but that within cer-
TABLE 1
Composition of Nutrient Solutions Employed by Early Investigators* f
Sachs's solution /
(1860)
Knop's solution
(1865)
Pfeffer's solution
(1900)
Crone's solution
(1902)
Ingredient
Grams
per 1,000 cc
H20
Ingredient
Grams
per 1,000 cc
H2O
Ingredient
Grams
per 1,000 cc
H2O
Ingredient
Grams
per 1,000 cc
H20
KNOs
1.00
Ca(N03)2
0.8
Ca(N03)2
0.8
KNOa
1.00
Ca3(P04)2
0.50
KNO3
0.2
KNOa
0.2
Ca3(P04)2
0.25
MgS04
0.50
KH2PO4
0.2
MgS04
0.2
MgSC-4
0.25
CaS04
0.50
MgSO*
0.2
KH2PO1
0.2
CaSC-4
0.25
NaCl
0.25
FeP04
Trace
KC1
0.2
FePC-4
0.25
FeSO*
Trace
FeCla
Small
amount
* These and other formulas are given in: Miller, E. C. Plant physiology, p. 195-97. McGraw-Hill Book
Co., New York, N.Y. 1931.
t For best results, these solutions should be supplemented with boron, manganese, zinc, copper, and
molybdenum; see discussion in the text, pp. 35-37.
tain ranges of composition and total concentration, fairly wide latitude
exists in the nutrient solutions suitable for plant growth. Thus Sachs
wrote :
I mention the quantities (of chemicals) I am accustomed to use generally in water
cultures, with the remark, however, that a somewhat wide margin may be permitted
with respect to the quantities of the individual salts and the concentration of the
whole solution — it does not matter if a little more or less of the one or the other salt
is taken — if only the nutritive mixture is kept within certain limits as to quality and
quantity, which are established by experience.
Until recently, the water-culture technique was employed exclusively
in small-scale, controlled laboratory experiments intended to solve fun-
damental problems of plant nutrition and physiology. These experiments
have led to the determination of the list of chemical elements essential
for plant life. They have thus profoundly influenced the practice of soil
management and fertilization for purposes of crop production.5 In re-
cent years, great refinements in water-culture technique have made pos-
5 However, nutrient solutions such as are employed in water-culture experiments
are not applied directly to soils. For discussion of fertilizer problems consult:
Hoagland, D. K. Fertilizer problems and analysis of soils in California. California
Agr. Exp. Sta. Cir. 317:1-15. Eevised 1938.
8 University of California — Experiment Station
sible the discovery of several new essential elements. These, although
required by plants in exceedingly small amounts, often are of definite
practical importance in agricultural practice. The elements derived from
the nutrient medium that are now considered to be indispensable for the
growth of higher green plants are nitrogen, phosphorous, potassium,
sulfur, calcium, magnesium, iron, boron, manganese, copper, and zinc.
New evidence suggests that molybdenum may have to be added to the
list.6 Present indications are that further refinments of technique may
lead to the discovery of still other elements, essential in minute quantity
for growth.
In addition to the list of essential elements, which is obviously of first
importance in making artificial culture media for growing plants, a
large amount of information has been amassed on the desirable propor-
tions and concentrations of the essential elements, and on such physical
and chemical properties of various culture solutions as acidity, alkalin-
ity, and osmotic characteristics. A most important recent development
in water-culture technique has been the recognition of the importance for
many plants of special aeration of the nutrient solution, to supplement
the oxygen supply normally entering the solution when in free contact
with the surrounding atmosphere.
The recently publicized use of the water-culture technique for com-
mercial crop production does not rest on any newly discovered principles
of plant nutrition other than those discussed above. It involves rather,
the application of a large-scale technique, developed on the basis of an
understanding of plant nutrition gained in previous investigations con-
ducted on a laboratory scale. The latter have provided knowledge of the
composition of suitable culture solutions. Furthermore, methods of con-
trolling the concentration of nutrients and the degree of acidity are,
except for modifications imposed by the large scale of operations, similar
to those employed in small-scale laboratory experiments.
The selection of a particular type of covering for the tanks adapted to
large-scale water-culture operations and of methods for supporting the
plants depends on the kind of plant. For example, in growing potatoes by
the water-culture method, provision must be made for a suitable bed
above the level of the solution, in which tubers can develop. On the other
hand, in growing tomatoes, it is only necessary to provide adequate sup-
port for the aerial portion of the stem, assuming that the roots are in a
favorable culture-solution medium, adequately aerated, and with light
excluded; a porous bed may be convenient as a means of facilitating
aeration of the solution, as a heat insulator, or as a support for the plant,
6 Unpublished data of D. I. Arnon and P. R. Stout.
Cm. 347]
Water- Culture Method
but plays no indispensable role. Aside from such considerations, the
choice of a covering is determined largely by expense and convenience,
provided the materials used are not toxic to plants.
With any kind of covering for the tanks, an adequate supply of air to
the roots must be provided. While the use of a porous bed instead of a
perforated cover facilitates aeration of roots, the bed can be dispensed
with if provision is made to bubble air through the nutrient solutions
Fig. 2. — The use of the water-culture technique for studying the nutritional
responses of lettuce plants under controlled conditions. The individual plants
are supported in corks which are placed in holes drilled in the metal covers. The
glass and rubber tubes carry air under pressure, which is bubbled through the
nutrient solution in the tanks.
(fig. 2) . Recent experiments have shown that even with the use of a por-
ous bed, bubbling air through the solution may be advantageous or,
under some conditions, indispensable.
As illustrations of some scientific problems of plant nutrition which
have been elucidated by the aid of the water-culture method of experi-
mentation, the effects of aeration of the roots on plant growth are shown
in plate 1, A and the foliage symptoms of deficiencies of mineral elements
required in large or minute quantity in plate 1,2? and plates 2 to 4.
The method of water culture is, as previously indicated, not the only
one for growing plants without soil. Several other experiment stations
have developed large-scale techniques of sand or gravel culture. These
involve the periodic flooding or subirrigation of a solid medium with
10 University of California — Experiment Station
nutrient solutions similar to those employed in the water-culture method.
Some investigators hold the opinion that the sand- or gravel-culture
methods have certain advantages in practical use over the water-culture
method, particularly in respect to conditions for aeration of the root
system.7
PRINCIPLES AND APPLICATION OF THE WATER-CULTURE
METHOD
The purpose of this circular is to give an account of the water-culture
method as a means of supplying mineral nutrients and water to plants.
The absorption of nutrient salts and water are only two of the physio-
logical processes of the plant. In order to evaluate the possibilities and
limitations of any special technique for growing plants, one has to under-
stand the significance of other interrelated processes, especially photo-
synthesis, respiration, transpiration, and reproduction.
IMPORTANCE OF CLIMATIC REQUIREMENTS
Many inquiries have been received on the possibility of growing plants
in water culture in dimly lighted places, or at low temperatures, under
conditions which would prevent growth of plants in soil. Obviously, no
nutrient solution can act as a substitute for light and suitable tempera-
ture. If there is doubt of the suitability of a particular location or season
for the growth of any kind of plant, a preliminary experiment should be
made by growing the plant in good garden soil. If the plant fails to make
satisfactory development in the soil medium because of unfavorable
light or temperature, failure may also be expected under water-culture
conditions.
Sunlight and suitable temperatures are essential for green plants, in
order that they may carry on one of the fundamental processes of plant
growth, known as "photosynthesis." In this process, the element carbon,
which forms so large a part of all organic matter, is fixed by plants from
the carbon dioxide of the atmosphere. This reaction requires a large
amount of energy, which is obtained from sunlight.
7 Further information on the sand- and gravel-culture methods may be obtained
from the following publications :
Withrow, R. B., and J. P. Biebel. Nutrient solution methods of greenhouse crop
production. Indiana (Purdue Univ.) Agr. Exp. Sta. Cir. 232:1-16. 1937.
Biekart, H. M., and C. H. Connors. The greenhouse culture of carnations in sand.
New Jersey Agr. Exp. Sta. Bui. 588:1-24. 1935.
Shive, J. W., and W. E. Bobbins. Methods of growing plants in solution and sand
cultures. New Jersey Agr. Exp. Sta. Bui. 636:1-24. 1938.
Eaton, Frank M. Automatically operated sand-culture equipment. Journal of Agri-
cultural Research 53:433-44. 1936.
Chapman, H. D., and George F. Liebig, Jr. Adaptation and use of automatically
operated sand-culture equipment. Journal of Agricultural Research 56:73-80. 1938.
Cm. 347] Water-Culture Method 11
Plants depend on photosynthesis for their food, that is, organic sub-
stances, such as carbohydrates, fats, and proteins, which provide them
with energy and enter into the composition of plant substance. The min-
eral nutrients absorbed by roots are indispensable for plant growth, but
they do not supply energy, and in that sense, cannot be regarded as
"plant food." Animal life is also absolutely dependent on the ability of
the green plant to fix the energy of sunlight.
TEMPERATURE RELATIONS
An earlier report of a preliminary experiment by other investigators
suggested that under greenhouse conditions heating the nutrient solu-
tion would produce large increases in the yield of tomatoes.8 Experi-
ments that we have carried on with tomatoes in a Berkeley greenhouse
(unheated except on a few occasions to prevent temperatures from fall-
ing below 50-55° Fahrenheit) have now given evidence that under the
climatic conditions studied, the beneficial effects of heating the nutrient
solution (to 70° F in the fall-winter and to 75° F in the spring-summer
period) are not of significance. If favorable air temperatures are main-
tained, there seems to be no need to heat the solution. Attempts should
not be made to guard against frost injury or unfavorable low air tem-
peratures merely by heating the nutrient solution. Proper provision
should be made for direct heating of the greenhouse. This may be found
desirable even when danger from low temperatures is absent, in order to
control humidity and certain plant diseases.
These experiments on tomatoes suggest that if greenhouse tempera-
tures are properly controlled, the solution temperature will take care of
itself. Certainly no expense, either in a greenhouse or outdoors, should
be incurred for equipment for heating solutions until experimentation
has shown that such heating is profitable. There is no one best solution
temperature. The physiological effects of the temperature of the solution
are interrelated with those of air temperature and of light conditions.
Most amateurs who try the water-culture method will grow plants in
warm seasons and probably will not wish to complicate their installation
by the addition of heating devices. Anyone who desires to test the influ-
ence of heating the culture solution should make comparisons of plants
grown under exactly similar conditions, except for the difference of tem-
perature in the solutions.
COMPARISON OF YIELDS BY SOIL AND WATER CULTURE
The impression conveyed by most of the popular discussions of the
water-culture method is that much more can be produced on a given
8 Gericke, W. F., and J. R. Tavernetti. Heating of liquid culture media for tomato
production. Agricultural Engineering 17:141-42, 184. 1936.
12 University of California — Experiment Station
surface of nutrient solution than on an equivalent surface of soil, even
under the best soil conditions feasible to maintain. Often quoted is the
yield of tomato plants grown for a twelve months' period in a greenhouse
water-culture experiment in Berkeley.9 This yield is compared with
average yields of tomatoes under ordinary field conditions, and the yield
from the water-culture plants is computed to be many times greater. But
closer analysis shows that mistaken inferences may be drawn from this
comparison. Predictions concerning yields in large-scale production are
of doubtful validity when based on yields obtained in small-scale experi-
ments under laboratory control. In any event, there is little profit in com-
paring an average yield from unstaked tomato plants grown during a
limited season under all types of soil and climatic conditions in the field,
with yields from staked plants grown in the protection of a greenhouse
for a full year. Evidence has long been available that yields of tomatoes
grown in a greenhouse, in soil, can far exceed yields obtained in the field.
It is true that in one series of outdoor experiments, the yields of tomatoes
under water-culture conditions were reported to be much higher than
under ordinary field conditions, on a unit-surface basis ; but again, the
general cultural treatment of the plants (especially with regard to
spacing and staking) was so different that comparisons of yield do not
mean very much. Furthermore, the equipment for an acre of water-
culture plants would be very costly, and technical supervision of the
cultures and the labor of staking vines would necessitate large and as yet
unpredictable expenditures.
A real test of the relative capacities of soil and water-culture media
for crop production requires that the two types of culture be carried on
side by side, with similar spacing of plants and with the same cultural
treatment otherwise. The soil should be of suitable depth and have its
nutrient supplying power and physical condition as favorable for plant
growth as possible. We initiated an experiment of this kind in Berkeley
late last summer, with the tomato as the test plant. The experiment has
now been carried on over a full year, and several of the conclusions de-
rived from it warrant emphasis. The yield of tomatoes grown by the
usual tank-culture technique was larger than any heretofore reported as
obtained by this method. The yield from the soil-grown plants, however,
was not markedly different from that of the plants grown by the tank
method (fig. 3). When the greenhouse yields of tomatoes from either
soil- or solution-grown plants were computed on an acre basis and com-
pared with average yields of field-grown tomatoes, the greenhouse plants
9 Gericke, W. F., Crop production without soil. Nature 141:536-40. 1938.
See also the article cited in footnote 8, p. 11.
ClR. 347J
Water- Culture Method
13
gave far greater yields. But as already suggested, such comparisons have
no direct practical significance because of the differences of climatic
factors, cultural practice, and length of season in the greenhouse and in
the open field.
Fig. 3. — Growth of tomato plants in fertile soil, in nutri-
ent solution, and in pure silica sand irrigated each day
with nutrient solution. Fruit had been harvested for 7
weeks prior to taking the photograph. All plants have
made excellent growth and set large amounts of fruit in
all three media. The general cultural conditions — spacing,
staking, etc. — were the same.
In one California commercial greenhouse, the yields of tomatoes grown
in soil were of the same magnitude as those obtained in a successful com-
mercial greenhouse employing the water-culture procedure, and in an-
other greenhouse using soil the yields were larger.
14
University of California — Experiment Station
Recently , data have become available on yield of potatoes grown in a
bed of peat soil in Berkeley. This yield was as large as any heretofore re-
ported as produced by the water-culture method.
r ji
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Fig. 4. — Under favorable conditions, tomato plants can grow to a great
height and bear fruit over an extended period of time. This is equally possible
in soil, sand, and water-culture media. The plants in the foreground were grown
in a bed of fertile soil. At the time of taking this photograph, several days
before the termination of the experiment, most of the fruit had already been
harvested.
The suggestion has sometimes been advanced that plants can be grown
more closely spaced in nutrient solutions than in soil, but no convincing
Cm. 347] Water-Culture Method 15
evidence of this has been given. In our experiments, we were able to grow
tomato plants as close together in the soil as in the solution (fig. 3) . The
density of stand giving the highest yields would be determined by the
adequacy of the light received by the plants when growth is not limited
by the supply of nutrients or water derived from either soil or nutrient
solution. Closeness of spacing under field conditions is of course limited
by practical considerations involving cost of crop production. This con-
sideration of economic factors and of the adequacy of light for plant
growth does not justify the view that the water-culture medium is better
adapted than soil to growing several different crops simultaneously in
the same bed.
Published pictures of tomato plants grown in water culture show im-
pressive height, and this growth in length of vines is frequently the sub-
ject of popular comment. As a matter of fact, the ability of tomato vines
to extend is characteristic of the plant and not peculiar to the water-
culture method. Staked plants grown for a sufficiently long period in a
fertile soil, under favorable light and temperature conditions, can also
reach a great height and bear fruit at the upper levels (fig. 4) . In com-
mercial greenhouse practice, growers usually "top" the vines. Fruit de-
veloped at higher levels is likely to be of inferior quality, and relatively
expensive to produce because of labor required to attach supports to the
vines and the inconvenience of harvesting. Furthermore, it may become
profitable to discontinue the tomato harvest when prices become low in
the summer and use the greenhouse space to plant another crop for the
winter harvest.
There is no magic in the growth of plants in water culture. This is only
another way of supplying water and essential mineral elements to the
plant. Land plants have become adapted to growing in soils during their
evolutionary history, and it is not reasonable to expect some extraordi-
nary increase in their potentialities for growth when an artificial me-
dium is substituted for soil. If no toxic conditions are present and a fully
adequate supply of water, mineral salts, and oxygen is provided to the
root system, either through an artificial nutrient solution or a soil, then
in the absence of plant diseases and pests, the growth of a plant is lim-
ited by its inherited constitution and by climatic conditions.
NUTRITIONAL QUALITY OF PLANT PRODUCT
Modern research on vitamins and on the role of mineral elements in ani-
mal nutrition has justly aroused great public interest. But unfortunately
one of the results is much popular discussion of diets and their influence
on health which is without scientific basis. It is, therefore, not unexpected
16 University of California — Experiment Station
that claims have been advanced that food produced by the water-culture
method is superior to that produced by soil.
As part of our investigation, careful studies of chemical composition
and general quality have been made on tomatoes of several varieties
grown in a fertile soil, and in sand- and water-culture media, side by side
in the same greenhouse, and with the same general cultural treatment.
No significant difference has been discovered in the mineral content of
the fruit developed on plants grown in the several media. (There is no
scientific basis for referring to tomatoes grown in water culture as
"mineralized.")
Neither could any significant difference be found in content of vita-
mins (carotene, or provitamin A, and vitamin C). Tomatoes harvested
from the soil and water cultures could not be consistently distinguished
in a test of flavor and general quality.10
Concerning the mineral content of tomatoes, it may further be added,
as a point of general interest, that all tomatoes contain but small amounts
of calcium and are not an important source of this mineral element in
the diet.
The similarity in composition and general quality of the tomatoes
grown in soil and water culture in the present experiments, is explained
by the fact that the climate and time of harvest were comparable and
the supply of mineral nutrients adequate in both cases. Whether plants
are grown in soil or water culture, climate and time of harvest are, of
course, of greatest importance in influencing quality and composition of
plant product.
Claims of unusual nutritional value for food products from certain
sources should not be accepted unless supported by results obtained in
research institutes of high standing.
PRESENT STATUS OF THE COMMERCIAL WATER-CULTURE METHOD
What is the justification for considering the water-culture method as a
means of commercial crop production ? The answer to this question is
that the method has certain possibilities in the growing of special high-
priced crops, particularly out of season in greenhouses in localities
where good soil is not available, or when maintenance of highly favorable
soil conditions is found too expensive. Soil beds in greenhouses often be-
come infected with disease-producing organisms, or toxic substances may
accumulate. Installation of adequate equipment for sterilizing soils and
operation of the equipment may require considerable expense. Also, in
10 The quality tests were conducted by Dr. Margaret Lee Maxwell of the Division
of Home Economics, and the carotene determinations were made by Dr. Gordon
Mackinney of the Division of Fruit Products, College of Agriculture.
Cm. 347] Water-Culture Method 17
theory at least, a water-culture medium, when expertly supervised,
should be subject to more exact control than a soil medium.
Present information does not warrant a prediction as to how widely
the water-culture method will find practical application in greenhouses.
One firm in California has reported success with this method in the pro-
duction of tomatoes ; another California firm, which invested a large sum
in equipment, met such serious difficulties that the equipment was not
being utilized at last report. We suggest that those who plan to use the
water-culture method for commercial purposes, make a preliminary test
with a few tanks of solution to compare the yields from soil and water-
culture media, and to learn some of the requirements for control of the
process. However, without some expert supervision, commercial success
is unlikely.
Indispensable to profitable crop production by the water-culture
method is a general knowledge of plant varieties, habits of growth, and
climatic adaptations of the plant to be produced, pollination, and control
of disease and insects; in other words, the same experience now needed
for successful crop production in soils.
The above discussion is primarily based on experiments with green-
house crops. Conceivably, in regions highly favored climatically, and
with a good water supply available, but where soil conditions are ad-
verse, some interest may arise in the possibilities of growing crops out-
doors, commercially, by the water-culture method. What crops, if any,
could be profitably grown by this method would depend on the value of
the crop in the market served, in relation to cost of production, which
would include a large outlay for tanks and other equipment and mate-
rials, as well as special costs of supervision and operation. Thus far, no
evidence is available on which to base any prediction as to future devel-
opment of the water-culture method of crop production under outdoor
conditions. Before planning any investment in this field, the most careful
consideration should be devoted to the economic and technical factors
concerned. It seems improbable, in view of the present cost of a commer-
cial water-culture installation, that crops grown by this method could
compete with cheap field-grown crops.
Recently, popular journals have discussed a project for growing vege-
tables in tanks of nutrient solution on Wake Island, in mid-Pacific, to
supply fresh vegetables (which constitute only a small proportion of the
total food requirements) for the inhabitants of the island and for passen-
gers of the clipper airships. This, however, is a special case, and there is
no reason to assume that it has any general agricultural significance.
18 University of California — Experiment Station
GROWING OF PLANTS IN WATER CULTURE BY AMATEURS
Most numerous among the inquiries for information about the water-
culture method are those from persons who wish to grow plants in this
way as a hobby. These persons usually seek exact directions as to how to
proceed to carry on water cultures. For reasons which, we hope, will be
made clear through reading this circular, it is not possible to describe a
general procedure that will insure success. Many technical difficulties
may be met : character of water, adjustment of acidity of the solution,
toxic substances from tanks or beds, uncertainty as to time for replenish-
ing salts in the nutrient solution, or for changing the solution, and the
like.
Why, it may be asked, do not most of these technical difficulties of the
water-culture method arise when plants are grown in soil ? Because in a
naturally fertile soil, or one which can be made fertile by simple treat-
ment, there occurs an automatic adjustment of many of the factors de-
termining the nutrition of the plant.
Some amateurs have recently reported results satisfactory to them-
selves, with certain kinds of plants grown in water culture, and similar
success can presumably be achieved by others through a fortunate com-
bination of nutritional and climatic conditions. Yet without knowledge
and control of the factors involved, no assurance can be given that suc-
cess with one kind of plant at one season can be consistently repeated
with other kinds of plants, or at other seasons. True, not every successful
gardener has a thorough training in plant and soil science. Nor can such
training, by itself, always insure success in gardening. However, since
the growing of plants in soil is one of the oldest occupations of mankind,
the gardener can often obtain guidance based on a rich store of accumu-
lated experience. Such experience is lacking for the growth of plants by
the water-culture method.
In any case, growing of plants as a hobby, in either soil or culture solu-
tion, without regard to cost of labor and materials, is of course a very
different matter from producing crops for profit. The experience of the
amateur gardener, whether he uses soil or the water-culture method, is
not adequate preparation for commercial crop production.
USE OF PREPARED SALT MIXTURES
Many amateurs have become interested in the purchase of mixtures of
nutrient salts ready for use, and various individuals and firms have
offered for sale small packages of salt mixtures. Clearly a prepared salt
mixture does not obviate the difficulties which may be met in growing
plants in water culture. Recently, some firms have made highly mislead-
Plate 1. — A, B, Effect of forced aeration on asparagus plants grown in culture solu-
tions: A, plants grown in solution through which air was bubbled continuously; B, plants
without forced aeration.
O, Asparagus plants grown in a nutrient solution in which boron, manganese, zinc, and
copper were present in such small amounts as one part in several million parts of solution ;
D, plants grown in solutions to which these elements were not added.
[19
• <"
c
Plate 2. — Symptoms of mineral deficiencies shown by tomato plants: A, complets nutri-
ent solution; B, solution lacking nitrogen; C, solution lacking phosphorus; D, solution
lacking potassium.
[20]
H
Plate 3. — Symptoms of mineral deficiencies shown by tomato plants : E, solution lacking
calcium ; F, solution lacking sulfur ; O, solution lacking magnesium ; H, solution lacking
boron.
[21]
Plate 4. — Symptoms of mineral deficiencies shown by tomato plants: A,
right, iron deficiency; left, complete nutrient solution; B, left, Manganese de-
ficiency; right, complete nutrient solution; G, left, copper deficiency; middle,
complete nutrient solution; right, zinc deficiency; D, left, molybdenum defi-
ciency; right, complete nutrient solution. (Illustration from recent unpub-
lished results of D. I. Arnon and P. R. Stout.)
[ 22
Cir. 347] Water-Culture Method 23
ing claims for the salt mixtures they sell. The Station makes no recom-
mendation with regard to any salt mixture, and the fact that a mixture is
registered with the California State Department of Agriculture, as re-
quired by the law governing sale of fertilizers, implies no endorsement
for use of the product. The directions given later will, we hope, help the
amateur to prepare his own nutrient solutions.
COMPOSITION OF NUTRIENT SOLUTIONS
Thousands of requests have been received by the Station for formulas for
nutrient salt solutions. It is often supposed that some remarkable new
combination of salts has been devised and that the prime requisite for
growing crops in solutions is to use this formula. The fact is that there is
no one composition of a nutrient solution which is always superior to
every other composition. ^Plants have marked powers of adaptation to
different nutrient conditions. If this were not so, plants would not be
growing in varied soils in nature. We have already emphasized in the
historical sketch of the water-culture method that within certain ranges
of composition and total concentration, fairly wide latitude exists in the
preparation of nutrient solutions suitable for plant growth. Many varied
solutions have been used successfully by different investigators. Even
when two solutions differ significantly in their effects on the growth of a
particular kind of plant under a given climatic condition, this does not
necessarily mean that the same relation between the solutions will hold
with another kind of plant, or with the same kind of plant under another
climatic condition.
Another point concerning nutrient solutions needs to be stressed.
After plants begin to grow, the composition of the nutrient solution
changes because the constituents are absorbed by plant roots. How rap-
idly the change occurs depends on the rate of growth of the plants and
the volume of solution available for each plant. Even when large volumes
of solutions are provided, some constituents may become depleted in a
comparatively short time by rapidly growing plants. This absorption of
nutrient salts causes not only a decrease in the total amounts of salts
available, but a qualitative alteration as well, since not all the nutrient
elements are absorbed at the same rates. One secondary result is that the
acid-base balance (pH) of the solution may undergo changes which in
turn may lead to precipitation of certain essential chemical elements
(particularly iron and manganese) so that they are no longer available
to the plant. Also to be considered are the effects of salts added with the
water (discussed later). ^
For these various reasons, the maintenance of the most favorable
24 University op California — Experiment Station
nutrient medium throughout the life of the plant involves not merely the
selection of an appropriate solution at the time of planting, but also con-
tinued control, with either the addition of chemicals when needed or re-
placement of the whole solution from time to time. Proper control of
culture solutions is best guided by chemical analyses of samples of the
solution taken periodically and by observations of the crop. Further in-
vestigation will determine if successful standardized procedures requir-
ing only limited control and adjustments can be developed for a given
crop, locality, and season of the year.
The plant physiologist, in his experiments, prepares his solutions with
distilled water, for the purpose of exact control. The commercial grower,
or the amateur, i^ usually limited to the use of domestic or irriga-
tion water which contains various salts, including sodium salts, such as
sodium chloride, sodium sulfate, and sodium bicarbonate, as well as cal-
cium and magnesium salts. Most waters suitable for irrigation or for
drinking can be utilized in the water-culture method, but the adjustment
of the reaction (pH) in the nutrient solution depends on the composition
of the water. Some waters may contain so much sodium salt as to be unfit
for making nutrient solutions. Even with a water only moderately high
in salt content, the salt may concentrate in the nutrient solution with
possibly unfavorable effects on the plant, if large amounts of water have
to be added to the tanks and the solutions are not changed. Also we have
had experience with a well water which was highly toxic because it con-
tained too high a concentration of zinc, apparently derived largely from
circulation through galvanized pipes. The water was, however, not in-
jurious to tomato plants when used on a soil, because of the absorbing
power of the soil for zinc.
As already indicated, the successful growth of a crop is dependent on
sunlight and temperature and humidity conditions, as well as on the
supply of mineral nutrients furnished by the culture medium. Complex
interrelations exist between climatic conditions and the utilization of
these nutrients. The relation of nitrogen nutrition and climatic condi-
tions to f ruitfulness has often been stressed. In some localities, deficient
sunshine may prevent the production of profitable greenhouse crops of
many species, in winter months, no matter what nutrient conditions are
present in the culture solution.
NUTRIENT REQUIREMENTS OF DIFFERENT KINDS OF PLANTS
The question is frequently asked : Does each kind of plant require a dif-
ferent kind of nutrient solution f The answer is that if proper measures
are taken to provide an adequate supply of nutrient elements, then many
Cm. 347] Water- Culture Method 25
kinds of plants can be grown successfully in nutrient solutions of the
same initial composition. (The same fertile soil can produce high yields
of many kinds of plants.)
The composition of the nutrient solution should always be considered
in relation to the total supply as well as the proportions of the various
nutrient elements. To give a specific illustration : assume that several
investigators prepare nutrient solutions of the same formula, but one
uses 1 gallon of the solution for growing a certain number of plants, an-
other 5 gallons of solution, and still another 50 gallons of solution. If
plants were grown to large size, each investigator would reach a different
conclusion as to the adequacy of the nutrient solution employed, al-
though the initial composition was the same in all cases. The investigator
using the small volume might find that his plants became starved for
certain nutrients while the one using the larger volume experienced no
such difficulty. In fact, the precise initial composition of a culture solu-
tion has very little significance, since the composition undergoes contin-
uous change as the plant grows and absorbs nutrients. The rate and
nature of this change depends on many factors, including total supply of
nutrients. Adequacy of supply of nutrients involves volume of solution
in relation to the number of plants grown, stage of growth of the plant
and rate of absorption of nutrients, and frequency of changes of solution.
Apart from the question of adequate supply of nutrients, there are
certain special responses of different species of plants which have to be
taken into account in the management of nutrient solutions. Plants vary
in their tolerance to acidity and alkalinity. They also differ in their
susceptibility to injury from excessive concentrations of elements like
boron, manganese, copper, and zinc. Some plants may be especially prone
to yellowing because of difficulty in absorbing enough iron or manganese.
Some may succeed best in more dilute nutrient solution than is employed
for most kinds of plants. Unfavorable responses by certain plants to high
nitrogen supply, in relation to fruiting, under certain climatic condi-
tions, may require consideration.
Since the adaptation of a nutrient solution to the growth of any par-
ticular kind of plant depends on the supply of nutrients and on climatic
conditions, there is no possibility of prescribing a list of nutrient solu-
tions, each one best for a given species of plant." Some general type of
solution, such as those described in this circular, should be tried first. It
may be modified later if found necessary by experiment.
11 A number of inquiries have been received regarding the culture of mushrooms.
The water-culture method under discussion is unsuited to the culture of mushrooms.
These plants require organic matter for their nutrition, and differ in this way from
green plants, which can grow in purely mineral nutrient solutions like those described
in this circular.
26 University of California — Experiment Station
NUTRIENT DEFICIENCIES, INSECT ATTACKS, AND DISEASES
Marked deficiencies of various nutrient elements are reflected in symp-
toms appearing in the leaves and other parts of the plants. A series of
photographs (plates 2 to 4) shows the general character of foliage symp-
toms for deficiency of each essential element as developed by the tomato
plant.
Contrary to some statements, it is not true that plants grown by the
water-culture method are thereby protected against diseases (except
strictly soil-borne diseases) or the attacks of insects. Recent observations
suggest that diseases peculiar to water culture may sometimes attack
plants grown in nutrient solutions.
WATER REQUIREMENTS OF PLANTS GROWN BY THE
WATER-CULTURE METHOD
The use of water by plants is primarily determined by the physiological
characteristics of each species of plant, extent of leaf surface, and atmos-
pheric conditions, just as when plants are grown in soil. If a large crop is
produced, either by the water-culture method or in soil, and if climatic
conditions favor high evaporation of water from the plant, the amount of
water used in producing the crop is necessarily large.
In a greenhouse experiment conducted in Berkeley for the purpose of
comparing the growth of tomatoes in soil and water-culture media, ac-
cording to actual measurement, somewhat more water was required to
produce a unit weight of fruit under water-culture conditions than under
soil conditions. The principal loss of water is by evaporation through the
plant, and that is common to both soil and water culture ; but possibly
more water was evaporated from the water surface than from the soil
surface. The fallacy of the idea that plants could be grown in a desert
region with a fraction of the water needed to produce crops in irrigated
soil is evident, if reasonably good management of irrigation practices is
assumed.
RESUME OF THE WATER-CULTURE TECHNIQUE
Many types of containers for nutrient solutions have been found useful.
In investigational work, 1- or 2-quart Mason jars provided with cork
stoppers often serve as culture vessels (fig. 5) . Sometimes 5- or 10-gallon
earthenware jars have been found suitable for experimental purposes.
Small tanks of various dimensions have been extensively used. For cer-
tain special investigations, shallow trays or vessels of Pyrex glass are
required. The selection of a container depends on the kind of plant to be
grown, the length of the growing period, and the purpose for which the
ClE. 347]
Water- Culture Method
27
plants are grown. Figure 7 shows the varied types of containers for
nutrient solutions as employed at the Station for research purposes.
Some of the smaller containers illustrated would doubtless be convenient
for amateur use, but the importance of the factor of aeration of the solu-
tion should be stressed. If small containers are employed and a large root
Fig. 5. — Corn and sunflower plants grown in nutrient
solution contained in 2-quart Mason jars. Note method of
placing plants in perforated corks. The jars are covered
with thick paper to exclude light.
system is to be developed, special aeration of the culture solutions may
be desirable or necessary. Plants differ greatly in regard to their require-
ments for aeration of the root system.
For commercial water culture, long, narrow, shallow tanks have been
employed. They may be constructed of wood, cement, black iron coated
with asphalt paint, or other sufficiently cheap materials which do not
give off toxic substances. In these tanks is placed the nutrient solution in
28 University of California — Experiment Station
which roots of the plant are immersed. Wire screens are placed over the
tops of the tanks, or inside, above the solution. The screens support a
layer of bedding of varying thickness (often 3 or 4 inches), according to
the kind of plant grown (fig. 6). This technique was first suggested by
W. F. Gericke.12 The bed may be prepared from a number of inexpensive
materials — for example, pine shavings, pine excelsior, rice hulls. Some
materials, such as redwood shavings or sawdust, may be toxic. Seeds are
Fig. 6. — General arrangement of tank equipment and method of planting:
A, a frame supporting a wire screen fits over the metal tank (fig. 7, A) filled
with the nutrient solution; B, tomato plants are placed with their roots im-
mersed in the nutrient solution ; a layer of excelsior is spread over the netting,
as shown in the far end of the tank ; C, the planting is completed by spreading
a layer of rice hulls over the excelsior.
planted in the moist beds, or young plants from flats are set in them with
their roots in the nutrient solution. Roots may later develop not only in
the solution in the tanks, but also in the beds.
The shallowness of the tanks and the porous nature of the beds facili-
tate aeration of the root system — an essential factor — but as already
pointed out, such aeration unsupplemented by an additional oxygen
supply, does not give the best growth of all kinds of plants. Recently evi-
dence became available that significant improvement of growth and
yield of tomato plants resulted from continuous bubbling of air through
12 Gericke, W. F. Aquaculture: a means of crop production. American Journal
of Botany 16:862. 1929.
Cir. 347] Water-Culture Method 29
the nutrient solution, although the yields from unaerated cultures were
at least as large as any previously reported for water culture.
Chemically pure salts commonly employed in making nutrient solu-
tions for scientific experiments would be too expensive for commercial
practice, and a number of ordinary fertilizer salts can serve in large-
scale production of crops. Recent developments in the fertilizer industry
have made available cheap salts of considerable degree of purity. Some
commercial salts, however, contain impurities (fluorine, for example, is
commonly found in phosphate fertilizers) which may be toxic to plants
under water-culture conditions.
DIRECTIONS FOR GROWING PLANTS BY THE WATER-
CULTURE METHOD
TANKS AND OTHER CONTAINERS FOR NUTRIENT SOLUTIONS
Various kinds of tanks have been utilized for growing plants in water
culture. Tanks of black iron, well painted with asphalt paint (most ordi-
nary paints cannot be used because of toxic substances), have proved
satisfactory for experimental work. Galvanized iron may give trouble,
even when coated with asphalt paint, if the paint scales off.
Concrete tanks have been tried, but they may require thorough leach-
ing before use. Painting the inside of the tank with asphalt paint is ad-
visable. Wooden tanks will serve the purpose, if made watertight. Red-
wood may give off toxic substances and therefore may require prelimi-
nary leaching to remove these substances. Finally, coating with asphalt
paint is desirable.
For small-scale cultures, 2- or 4-gallon earthenware crocks may be
serviceable. A wire screen to hold the bedding material can be bent over
the sides of the crock. But if a number of plants are to be grown to large
size in such jars, the solution may require special aeration as by bubbling
air through it (see p. 9) .
For demonstrations in schools, Mason jars covered with brown paper,
to exclude light, can be employed (fig. 5). The jars are provided with
cork stoppers in which one or more holes have been bored (sometimes a
slit is also made in the cork ; see fig. 1) . Plants are fixed in the holes with
cotton. Wheat or barley plants are very suitable for these demonstra-
tions, since they may be grown in the jars without any special arrange-
ments for aeration.
Other types of culture vessels are shown in figure 7.
The dimensions of tanks must be selected in accordance with the objec-
tive. One kind of tank, of moderate size, adapted to many purposes, is
30
University of California — Experiment Station
30 inches long, 30 inches wide, and 8 inches deep (fig. 2, p. 9, and fig.
7, B) . A smaller tank, 30 inches long, 12 inches wide, and 8 inches deep,
is convenient for use in many experiments (fig. 7, C) . In general, shallow
tanks will be found suitable. The length and width may be determined
by consideration of convenience and economy. As an alternative to the
porous bed, for many kinds of plants, tanks can be provided with metal
or wooden covers perforated to hold corks in which plants are fixed with
Fig. 7. — Various types of containers for carrying on water-culture experi-
ments :
A, Large iron (not galvanized) tank painted inside with asphalt paint, outside
with aluminum paint. Dimensions: 10 ft. x 2% ft. X 8 in. Shows one section of
metal cover. Perforated corks for supporting plants are fixed in the holes
(fig. 2). Wooden frames containing bedding material may also be set over
these tanks as shown in figure 6.
B, Iron tank of dimensions : 30 in. x 30 in. x 8 in.
C, Iron tank of dimensions : 30 in. X 12 in. x 8 in.
D, Iron tank of dimensions: 15% in. x 10% in. x 6 in.
E, Graniteware pan 16 in. X 11 in. x 2% in. used for growing small plants. Per-
forated metal covers as shown in A, C, and D may be used on all metal tanks or
trays. The number of holes in the cover can be varied according to the number
and size of plants to be grown.
F and G, Pyrex dish and beaker used for special experiments designed to
study the essentiality of certain chemical elements required by plants in minute
quantity, such as zinc, copper, manganese, and molybdenum. The covers for
these containers shown in the illustration, are molded from plaster of Paris
and then coated with paraffin.
cotton, if adequate aeration is maintained (fig. 2.)13 (See discussion of
aeration, p. 9.
When large tanks are to be used with a porous bed, a heavy chicken-
wire netting (1-inch mesh), coated with asphalt paint, is fastened to
a frame and placed directly over the tank to provide support for the
porous bed. In constructing a frame, it is advisable to leave several nar-
13 A description of the construction of aerating devises for culture solutions is
given by: Furnstal, A. P., and S. B. Johnson. Preparation of sintered Pyrex glass
aerators for use in water-culture experiments with plants. Plant Physiology 11:
189-94. 1936.
Cir. 347] Water-Culture Method 31
row sections not covered with wire netting, but with wooden covers
which can be conveniently removed for inspection of roots or for adding
water or chemicals. The wire netting should be stretched immediately
above the surface of the solution when the tank is full. Cross supports
may be placed under the netting to prevent it from sagging (fig. 6). A
carpenter or mechanic can design and build suitable tanks and frames,
which may take many forms.
NATURE OF BED14
When a porous bed is to be employed, a wire screen is covered by a layer
of the porous material 3 or 4 inches thick — thicker when tubers or fleshy
roots develop in the bed. Various cheap bedding materials have been sug-
gested : pine excelsior, peat moss, pine shavings or sawdust, rice hulls, etc.
Some materials are toxic to plants. Redwood should usually be avoided.
One type of bed which has produced no toxic effects in experiments car-
ried on in Berkeley, with tomatoes, potatoes, and certain other plants,
consists of a layer of pine excelsior 2 or 3 inches thick, with a superim-
posed layer of rice hulls about 1 or 2 inches thick. For plants producing
tubers of fleshy roots, some finer material may possibly need to be mixed
with the excelsior. This is also essential when small seeds are planted in
the bed, to prevent the seeds from falling into the solution and to effect
good contact of moist material with the seed. In all cases, the bed must be
porous and not exclude free access of air.
If seeds are planted in the bed, it must, of course, be moistened at the
start and maintained moist until roots grow into the solution below. For
the development of tubers, bulbs, fleshy roots, etc., the bed should be
maintained in a moist state, by occasional sprinkling. Great care should
be observed to prevent waterlogging of the bed, resulting from immer-
sion of the lower portion of the bed in the solution. This leads to exclusion
of air and to undesirable bacterial decompositions.
PLANTING PROCEDURES
Seeds may be planted in the moist bed, but often it is better to set out
young plants chosen for their vigor, which have been grown from seeds
in flats of good loam. Some seeds (for example, cereal seeds) may also be
conveniently germinated between layers of moist filter paper (or paper
toweling), particularly if plants are to be fixed in corks and grown in
jars or in tanks with perforated metal or wooden covers. The upper lay-
ers of moist paper are removed after seeds begin to germinate. The seed-
14 The general arrangement of this type of bed was described by : Gericke, W. F.,
and J. R. Tavernetti. Heating of liquid culture media for tomato production. Agri-
cultural Engineering 17:141-42, 184. 1936.
32 University of California — Experiment Station
lings are allowed to grow on the moist bed until large enough to place
in corks. An excess of water is then added to the moist paper and the
young plants removed carefully so as not to damage the roots.
In transplanting from a flat of soil, the soil is thoroughly soaked with
water so that the plants can be removed with the least possible injury to
the roots. The roots are then rinsed free of soil with a light stream of
water and immediately set out in the beds or corks, with the roots im-
mersed in the solution. When young plants are set out in the beds, the
roots are placed in the solution, and at the same time the layer of ex-
celsior is built up over the screen. Then the layer of rice hulls is placed
on top of the excelsior (fig. 6). If seeds are to be planted in the bed, the
whole bed must be installed and moistened before the seed is planted.
SPACING OF PLANTS
In our experiments with tomato plants, they were set close together, in
some instances 20 plants to 25 square feet of solution surface. No gen-
eral advice can be offered as to the best spacing. This depends on the kind
of plant and on light conditions. Individual experience must guide the
grower.
ADDITION OF WATER TO TANKS
In starting the culture, the tank is filled with solution almost to the level
the lower part of the bed. As the plants grow, water will be absorbed by
plants or evaporated from the surface of the solution, and the level of
the solution in the tank will fall. The recommendation has generally been
made that after the root system is sufficiently developed, the level of the
solution should remain from one to several inches below the lower part of
the bed, to facilitate aeration. However, since the solution level should not
be permitted to fall very far, regular additions of water are required.15
As pointed out earlier, when large amounts of water have to be added
to a tank, excessive accumulations of certain salts contained in the water
may occur, especially if the salt content of the water is high. To avoid
this difficulty, the entire solution is changed whenever the salt concen-
tration becomes high enough to influence the plant adversely. Should
plants be injured, however, by the presence in the water of high concen-
trations of elements like zinc, changing solutions will not prevent injury.
Because of the wide variation in the composition of water from different
sources, no specific directions to cover all cases can be given.
16 Certain methods of circulating culture solutions (such as those described by J. W.
Shive and W. R. Robbins, in the citation given in footnote 7, p. 10) may be convenient
for maintaining a supply of water and nutrients, as well as assisting in aeration of
roots. One commercial greenhouse concern has utilized on a large scale a method of
circulating nutrient solution from a central reservoir.
Cir. 347] Water-Culture Method 33
CHANGES OF NUTRIENT SOLUTION
As the plants begin to grow, nutrient salts will be absorbed and the
acidity of the solution will change. More salts and acid may be added,
but to know how much, chemical tests on the solution are required. When
these cannot be made, an arbitrary procedure may be adopted of drain-
ing out the old solution every week or two, immediately refilling the
tank with water and adding acid and salts as at the beginning of the cul-
ture. The number of changes of solution required will depend on the size
of plants, how fast they are growing, and on volume of solution. Dis-
tribute the acid and salts to different parts of the tank. In order to effect
proper mixing, it may be well to fill the tank at first only partly full (but
keep most of the roots immersed) and then after adding the acid and
salts, to complete the filling to the proper level with a rapid stream of
water, which should be so directed as not to injure the roots.
TESTING AND ADJUSTING THE ACIDITY OF WATER
AND NUTRIENT SOLUTION
Ordinarily some latitude is permissible in the degree of acidity (pH) of
the nutrient solution. For most plants, a moderately acid reaction (from
pH 5.0 to 6.5) is suitable. If distilled water is used in the preparation of
nutrient solution, no adjustment of its reaction is necessary. If tap
water is used, a preliminary test of its reaction should be made ; if the
water is found alkaline, it should be acidified before adding the nutrient
salts.
As already stated, the reaction (pH) of the nutrient solution is subject
to change as the plant grows. The reaction of the culture solution should
be tested from time to time and corrected if found alkaline.
The chemicals required for testing acidity of water or nutrient solu-
tion are :
1. Bromthymol blue indicator. This can be obtained, with directions
for use, from chemical supply houses, in the form of solutions or im-
pregnated strips of paper.
Strips of other test papers covering a wide range of acidity are also
now available on the market and may be found, by the amateur who un-
derstands their use, very convenient for adjusting the acidity of water
as well as that of the nutrient solution.
2. Sulfuric acid. Purchase a supply of 3 per cent (by volume) acid of
chemically pure grade. (Concentrated, chemically pure sulfuric acid
may be purchased and diluted to 3 per cent strength, but the concen-
trated acid is dangerous to handle by inexperienced persons.) This 3 per
34 University of California — Experiment Station
cent acid may be further diluted with water if a preliminary test indi-
cates that only small additions of acid are required to bring about a de-
sirable reaction.
Test the degree of acidity of a measured sample of the water or nu-
trient solution (a quart, for example) by noting the color of the added
indicator or test paper immersed in the solution. When bromthymol blue
indicator is used, a yellow color indicates an acid reaction (with no fur-
ther adjustment necessary) , green a neutral reaction, blue an alkaline
reaction.
If the original color is green or blue, add the dilute sulfuric acid (3
per cent or less in strength) slowly with stirring until the color just
changes to yellow (indicating approximately pH 6). Do not add more
beyond this point, since the yellow color will also persist when excessive
amounts of acid are added. Record the amount of acid required.
Finally, add a proportionate amount of the acid to the water or nu-
trient solution in the culture tank or vessel, having first determined how
much it holds.
MODIFICATION OF NUTRIENT SOLUTION BASED
ON ANALYSIS OF WATER
If tap water is used in making the nutrient solution, a chemical analysis
of it is useful. Some waters may contain so much calcium, and perhaps
magnesium and sulfate, that further additions of these nutrient elements
are unnecessary, or even undesirable. The objective should be to approxi-
mate the intended composition of the nutrient solution, taking into ac-
count the salts already present in the water. Since, however, considerable
latitude is permissible in the composition of nutrient solutions, analysis
of the water is not indispensable, unless the content of mineral matter is
very high.
SELECTION OF A NUTRIENT SOLUTION
As stated before, there is no one nutrient solution which is always supe-
rior to every other solution. Among many solutions which might be em-
ployed, those described below have been found to give good results with
various species of plants in experiments conducted in Berkeley, with a
source of good water. Other solutions can also be used with good results.
The composition of the solutions is given in two forms : (A) by rough
measurements adapted to the amateur without special weighing or meas-
uring instruments, and (B) in more exact terms for those with some
knowledge of chemistry, who have proper facilities for more accurate
experimentation. These facilities would include chemical glass-ware, a
chemical balance and a supply of C. P. chemicals.
Cir, 347]
Water- Culture Method
35
PREPARATION OF NUTRIENT SOLUTIONS: METHOD A,
FOR AMATEURS
Either one of the solutions given in table 2 may be tried. Solution 2 may
often be preferred because the ammonium salt delays the development of
undesirable alkalinity. The salts are added to the water, preferably in
the order given.
To either of the solutions, add the elements iron, boron, manganese,
and in some cases, zinc, and copper, which are required by plants in
minute quantities. There is danger of toxic effects if much greater quan-
TABLE 2
Composition of Nutrient Solutions*
(The amounts given are for 25 gallons of solution)
Salt
Grade
of salt
Approximate
amount,
in ounces
Approximate
amount, in
level tablespoons
Solution If
Technical
Fertilizer
Fertilizer
Technical
2
3
1
4 (of powdered salt)
7
4
Solution 2f
Technical
Fertilizer
Fertilizer
Technical
2V2
2
5 (of powdered salt)
Calcium nitrate
Magnesium sulfate (Epsom salt)
6
4
* The University does not sell or give away any salts for growing plants in water culture. Chemicals
may be purchased from local chemical supply houses, or possibly may be obtained through fertilizer
dealers. Some of the chemicals may be obtained from druggists. If purchased in fairly large lots, the present
price of the ingredients contained in 1 pound of a complete mixture of nutrient salts is approximately 5
to 10 cents for either solution described above.
f To either of these solutions, supplements of elements required in minute quantity must be added;
see directions in the text.
tities of these elements are added than those indicated later in the text.
Molybdenum and possibly other elements required by plants in minute
amounts will be furnished by impurities in the nutrient salts or in the
water, and need not be added deliberately.
a) Boron and Manganese Solution. — Dissolve 3 teaspoons of pow-
dered boric acid and 1 teaspoon of chemically pure manganese chloride
(MnCl2 • 4H20) in a gallon of water. (Manganese sulfate could be sub-
stituted for the chloride.) Dilute 1 part of this solution with 2 parts of
36 University of California — Experiment Station
water, by volume. Use a pint of the diluted solution for each 25 gallons
of nutrient solution.
The elements in group a are added when the nutrient solution is first
prepared and at all subsequent changes of solution. If plants develop
symptoms characteristic of lack of manganese or boron (see plate 4, B,
and plate 3, H), solution a, in the amount indicated in the preceding
paragraph, may be added between changes of the nutrient solution or
between addition of salts needed in large quantities.16 But care is needed,
for injury may easily be produced by adding too much of these elements.
b) Zinc and Copper Solution. — Ordinarily this solution may be omit-
ted, because these elements will almost certainly be supplied as impuri-
ties in water or chemicals, or from the containers. "When it is needed
(plate 4, C) additions are made as for solution a. To prepare solution b,
dissolve 4 teaspoons of chemically pure zinc sulfate (ZnS04 ■ 7H20) and
1 teaspoon of chemically pure copper sulfate (CuSo4 ■ 5H20) in a gallon
of water. Dilute 1 part of this solution with 4 parts of water. Use 1 tea-
spoon of the diluted solution for each 25 gallons of nutrient solution.
c) Additions of Iron to Nutrient Solution. — Generally, iron solution
will need to be added at frequent and regular intervals, for example, once
or twice a week. If the leaves of the plant tend to become yellow (see plate
4, A) , even more frequent additions may be required. However, a yellow-
ing or mottling of leaves can also arise from many other causes.
The iron solution is prepared as follows : Dissolve 1 level teaspoon of
iron tartrate (iron citrate or iron sulfate can be substituted, but the tar-
trate or citrate is often more effective than the sulfate) in 1 quart of
water. Add % cup of this solution to 25 gallons of nutrient solution each
time iron is needed.
PREPARATION OF NUTRIENT SOLUTIONS: METHOD B,
FOR SCHOOLS OR TECHNICAL LABORATORIES
For experimental purposes, the use of distilled water and chemically
pure salts is recommended. Molar stock solutions (except when otherwise
indicated) are prepared for each salt, and the amounts indicated below
are used.
Solution 1 cc in a liter of
nutrient solution
M KH2P04, potassium acid phosphate 1
M KN03, potassium nitrate 5
M Ca(N03)2, calcium nitrate 5
M MgS04, magnesium sulfate 2
18 The University is not prepared to diagnose symptoms on samples of plant tissues
sent in for examination.
Cir. 347] Water- Culture Method 37
Solution 2 cc in a liter of
nutrient solution
M NH4H2P04, ammonium acid phosphate 1
M KN03, potassium nitrate 6
M Ca(N03)2, calcium nitrate 4
M MgS04, magnesium sulfate 2
To either of these solutions add solutions a and b below.
a) Prepare a supplementary solution which will supply boron, man-
ganese, zinc, copper, and molybdenum, as follows :
Grams dissolved
Compound in 1 liter of H20
H3BO3, boric acid 2.86
MnCl2 • 4H20, manganese chloride 1.81
ZnS04 • 7H20, zinc sulfate 0.22
CuS04 • 5H20, copper sulfate 0.08
H2Mo04 • H20, molybdic acid (assaying 85 per cent Mo03) 0.09
Add 1 cc of this solution for each liter of nutrient solution, when solu-
tion is first prepared or subsequently changed, or at more frequent in
tervals if necessary.
This will give the following concentrations :
Parts per million of
Element nutrient solution
Boron 0.5
Manganese 0.5
Zinc 0.05
Copper 0.02
Molybdenum 0.05
b ) Add iron in the form of 0.5 per cent iron tartrate solution or other
suitable iron salt, at the rate of 1 cc per liter, about once or twice a week
or as indicated by appearance of plants.
The reaction of the solution is adjusted to approximately pH 6 by
adding 0.1 N H2S04 (or some other suitable dilution) .
Molar Solutions. — The concentrations of stock solutions of nutrient
salts used in preparation of nutrient solutions are conveniently ex-
pressed in terms of molarity. A molar solution is one containing 1 gram-
molecule (mol) of dissolved substance in 1 liter of solution. (In all nu-
trient-solution work, the solvent is water.) A gram-molecule or mol of a
compound is the number of grams corresponding to the molecular weight.
Example 1, how to make a molar solution of magnesium sulfate : The
molecular weight of magnesium sulfate, MgS04 ■ 7H20 is 246.50. One mol
of magnesium sulfate consists of 246.50 grams. Hence to make a molar
solution of magnesium sulfate, dissolve 246.50 grams of MgS04 ■ 7H20
in water and make to 1 liter volume.
Example 2, how to make a one-twentieth molar (0.05 M) solution of
38 University of California — Experiment Station
monocalcium phosphate, Ca(H2P04)2 ■ H20 (used in deficiency studies,
below) : The molecular weight of monocalcium phosphate, Ca(H2P04) 2 ■
252.17 grams
H20 is 252.17. Hence 0.05 mol of Ca(H2P04)2 • H20 is —
= 12.61 grams. Therefore, to make a 0.05 M solution of monocalcium
phosphate, dissolve 12.61 grams of Ca (H2P04) 2 • H20 in water and make
to 1 liter volume.
NUTRIENT SOLUTIONS FOR USE IN DEMONSTRATING
MINERAL DEFICIENCIES IN PLANTS
In any experiment to demonstrate mineral deficiencies in plants, solu-
tion 1 or solution 2 should be used as a control to show normal growth in
a complete solution. Below are given six solutions, each lacking in one
of the essential elements. Similar solutions were used in producing the
deficiency symptoms shown in plates 2 and 3, with plants which had pre-
viously been grown for several weeks in complete nutrient solutions.
Distilled water should be used in making these solutions.
a, Solution lacking nitrogen n«*» Jtoj^
0.5 M K2S04 5
M MgS04 2
0.05 M Ca(H2P04)2 10
0.01 M CaS04 200
6, Solution lacking potassium n «|y ^n
M Ca(N03)2 5
M MgS04 2
0.05 M Ca(H2P04)2 10
c, Solution lacking phosphorus n ~gn; nter^
M Ca(N03)2 4
M KN03 6
M MgS04 2
d, Solution lacking calcium nutrie/t loStfon
M KNO3 5
M MgS04 2
M KH2P04 1
e, Solution lacking magnesium nuctcr£nat ^t?0fn
M Ca (N03)2 4
M KNO:! 6
M KH2P04 1
0.5 M K2S04 3
Gir. 347] Water-Culture Method 39
f, Solution lacking sulfur n «•*■£ "J- &
M Ca(N03)2 4
M KN03 6
M KH2P04 1
M Mg(N03)2 2
To any of these solutions, add iron and the supplementary solution
suppying boron, manganese, zinc, copper, and molybdenum as previously
described (p. 37). For use with solution /, lacking sulfur, a special
supplementary solution should be prepared in which chlorides replace
the sulfates. Also, sulfuric acid should not be used in adjusting the
reaction of the nutrient solution.
In order to produce iron-deficiency symptoms, plants should be grown
in glass containers and no iron should be added to the otherwise complete
nutrient solution. Similarly, it may be possible to produce boron- or man-
ganese-deficiency symptoms with certain plants (tomatoes, for example)
by omitting either one of these elements from the supplementary solu-
tion. Zinc-, copper-, and molybdenum-deficiency symptoms can usually
be produced only by the use of a special technique, the description of
which exceeds the scope of this circular.
30m-l, '39(5984)
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